The efficacy for cancer therapy of radiation and drugs, such as cisplatin, is often limited by the development of resistance. Biochemistry and tissue culture studies indicate that such resistance is a function of the capacity of cancer cells to repair damaged DNA. Parent application Ser. No. 234,096, in accord with various published papers, demonstrates enhanced expression of DNA repair enzymes by DNA resistant phenotypes of certain human carcinoma cell lines. See, e.g., Lai, G. M., et al., Biochem. Pharmacol. 37:4597-4600 (1988); Hospers, G. A. P., et al., Cancer Res. 48:6803-6807 (1988); Masuda, H., et al., Cancer Res. 48:5713-5716 (1988); Kraker, A., et al., Cancer Lett. 38:307-314 (1988); Scanlon, K. J., et al., Cancer Investigation 7:563-589 (1989) (in press-incorporated herein by reference); and Scanlon, K. J., et al., Anticancer Res. 9:1301-1312 (1989) (incorporated herein by reference). See also, Murray, D., et al., Cancer Res. 45:6446-6452 (1985) and Miller, M. R., et al., J. Biol. Chem. 257:10204-10209 (1982).
AZT and various other nucleoside analogs are selective inhibitors of retroviral reverse transcriptases and of human DNA polymerases .alpha., .beta. and .gamma.. See White, E. L., Biochem. and Biophys. Res. Comm. 161:393-398 (1989); Swinnen, L. J., et al., Cancer Res. 49:1383-1389 (1989); Ahnstrom, G., Biochimica et Biophysica Acta 1007:357-358 (1989); Elion, G. B., Science 244:41-47 (1989); Lin, T. -S., et al., J. Med. Chem. 32:1891-1895 (1989); Liu, S. -Y., et al., Cancer Res. 49:1366-1370 (1989); Oho, K., et al., Mol. Pharmacol. 35:578-583 (1989); Yarchoan, R., et al., New Eng. J. Med. 321:726-738 (1989) and U.S. Pat. No. 4,861,759.